1. Field of the Invention
The present invention relates to novel compositions for topical application and delivery of a bio-affecting agent through the protective outer layer of the skin and into the underlying tissues or into the general circulation. More specifically, the invention relates to a composition comprising at least one bio-affecting agent and eucalyptol, and optionally, a nontoxic topical carrier and/or another penetration enhancer.
As used herein, the term "bio-affecting agent" refers to any chemical substance or formulation thereof which beneficially affects the mammalian body. Typically, the bio-affecting agent herein can be a "dermally effective dermatological agent" or a "systemically effective therapeutic agent". The term "dermally effective dermatological agent" as used herein refers to those chemical substances which when applied to mammalian skin exert a beneficial topical effect, which can be of a cosmetic nature (e.g., by protecting the skin against external factors or by improving appearance) or of a therapeutic nature (e.g., by attenuating the severity of a dermal disease). The term "systemically effective therapeutic agent" as used herein refers to those chemical substances which when administered by various routes such as intravenous infusion, intramuscular injection, oral, rectal or buccal routes, enter the general circulation and exhibit a therapeutic effect. The expressions "dermally effective dermatological agent" and "systemically effective therapeutic agent" are not intended to be mutually exclusive, however, it being recognized that a number of bio-affecting agents are indeed effective both dermally and systemically.
2. Description of the Prior Art
Eucalyptol is a well-known chemical compound which has long been used as an inhalational expectorant. It is also known by the names cineole and cajeputal. The art is also well-versed in the preparation of eucalyptol.
The skin of humans and other warm-blooded animals provides an excellent barrier to the penetration of exogenous chemical substances. The outer layer of the epidermis, called the stratum corneum, offers the maximum resistance to penetration, whereas the lower layers are relatively permeable. For proper treatment of dermal conditions, it is important that the active agent penetrate the stratum corneum where it is retained. From this reservoir in the outer layer, the bio-affecting agent is slowly released and penetrates the underlying areas where it exhibits its therapeutic or cosmetic effect. When dermatological agents such as sunscreens, which protect the underlying tissues from external factors (ultraviolet rays) are used, maximum retention in the stratum corneum is essential. On the other hand, the relative permeability of the layers of the epidermis below the stratum corneum can also allow access to the systemic circulation; indeed, it is necessary for the therapeutic agent to penetrate the stratum corneum in order to provide systemic therapeusis from the transdermal route.
It is well-known that the application of various therapeutic and cosmetic agents to the skin is useful for the treatment of a number of dermal conditions, e.g., hydrocortisone for pruritus and erythema in a topic dermatitis, erythromycin or tetracyclines for acne, 5-iodo-2'-deoxyuridine for herpes simplex, 5-fluorouracil for psoriasis and skin cancer, hydroquinone for lightening skin color and p-aminobenzoic acid for blocking the harmful rays of the sun.
It is also well-known that a number of therapeutically active agents, such as .beta.-blockers, antihypertensives, antiarrhythmics, antianginal agents, vasodilators, antiemetics, antibacterials, antifungals, corticosteroids, progestins, estrogens, androgens and antiinflammatories, when administered to warm-blooded animals by a number of various routes such as by intravenous infusion, intramuscular injection, oral, rectal or buccal routes, enter the general circulation and produce the appropriate systemic therapeutic effect. It is also known that the aforementioned methods of administration have certain disadvantages. For example, the intravenous and intramuscular routes are not only painful for the patient, but also must be performed by a trained individual. Buccal and rectal administration often produce discomfort and annoyances for the patient. Oral administration, although generally acceptable for the patient, often does not deliver the majority of the therapeutic agent to systemic circulation. This diminished drug delivery is usually attributed to poor absorption from the gastrointestinal tract and/or to degradation of the agent by the acidic medium of the stomach, by the enzymes in the gastrointestinal tract and surrounding tissue or by the rapid metabolizing enzymes of the liver through which the drug must pass before it enters the systemic circulation. For example, drugs such as anti-bacterials, narcotic analgesics, .beta.-blockers and others require relatively high doses when given orally due to the remarkable liver metabolism encountered. Effective delivery of such drugs through the skin would require much lower doses because the so-called "first pass" metabolism would be avoided.
Recognizing the fact that the outer layer of the skin, the epidermis, protects the area under the skin from the penetration of foreign chemicals, many investigators have turned to various enhancing agents, e.g., dimethylsulfoxide, dimethylformamide, methyldecylsulfoxide (U.S. Pat. No. 3,527,864) and dimethylacetamide (U.S. Pat. No. 3,472,931) in order to overcome the aforementioned problems and to deliver topically active agents more efficiently through the skin, as well as to enhance the absorption of systemically active therapeutic agents through the skin and into the general circulation. Dimethylsulfoxide, which is superior to both dimethylformamide and dimethylacetamide, has been shown to enhance the absorption through the skin of hydrocortisone and testosterone (Robert J. Feldmann and Howard I. Maibach, Proceedings of the Joint Conference on Cosmetic Science (1968), pages 189-203). Thus, the addition of dimethylsulfoxide to formulations of therapeutically active agents enhances the penetration of said agents through the skin and into the general circulation, thereby overcoming most of the aforementioned problems encountered by other routes of administration. Unfortunately, the use of dimethylsulfoxide is not without problems, for in addition to causing foul taste and body odor, it causes burning and erythema on the skin, activates latent virus infections within cells, reduces the relucency of the lens cortex and produces teratogenicity and tissue necrosis in animals. Compare Martindale, The Extra Pharmacopoeia, pages 1461-1463, Twenty-seventh Edition (1977), and the reference cited therein.
Thus, there exists a clear and present need for a novel agent to enhance the absorption through the skin of bio-affecting agents which is devoid of the disadvantages and drawbacks that to date have characterized the prior art enhancing agents.